PROJECT SUMMARY The primary goal of this project is to determine whether pathological forms of tau (pTau) ? a significant pathological hallmark of neurodegenerative tauopathies, can activate interleukin-1b (IL-1b) through MyD88- dependent nuclear factor-kB (NF-kB) and NLRP3-ASC inflammasome pathway to cause neuroinflammation, axonal and white matter pathology, synaptic loss and cognitive impairment. The goal is also to test the efficacy of a novel pTau-targeted virus-like particle (VLP)-based immunotherapy strategy against pTau-induced neuroinflammation in hTau model of tauopathy. Recent studies have suggested that once tau is hyperphosphorylated and misfolded, the neurons tend to expel pTau to the extracellular space, which is taken up by other neurons and results in trans-neuronal propagation of pTau. We made a compelling discovery that en route to other neurons, pTau can also interact with and serve as an initial trigger to lead to microglial activation and neuroinflammation. However, it is not clear how exactly pTau can induce innate immune activation within microglia. Our preliminary results suggest the possibility that neuronally-derived pTau upregulates microglial cell surface receptors like toll-like receptors (TLRs), engage MyD88 (a key adapter protein common for various TLRs and IL-1Rs), activate NF-kB and NLRP3-ASC inflammasomes and lead to maturation of IL-1b in microglia. Strikingly, suppression of pTau in vivo, microglial-specific deletion of MyD88 or ASC, significantly reduced IL-1b maturation. Intriguingly, clearing pTau via VLP-based vaccine reduces MyD88 expression, neuroinflammation, tau pathology and improves memory. Based on these preliminary observations we hypothesize that pTau activates NF-kB-NLRP3-ASC inflammasomes-IL-1b innate immune complex through TLR/MyD88-dependent pathway in microglia. Targeting pTau (by VLP-based immunotherapy), MyD88 or IL-1R1 accessory protein (IL- 1RAcP) at different levels of this cascade blocks the feed-forward induction of brain inflammation induced by tau. We will test this hypothesis under three Specific Aims. In the Specific Aim 1, we propose to determine if different forms of pTau from post-mortem human brains trigger NF-kB priming by MyD88 and IL-1b maturation by NLRP3-ASC-inflammasomes pathways. In Specific Aim 2, we propose to determine if pTau-induced progressive NF-kB activation, neuroinflammation, MRI-based structural alterations and cognitive dysfunction is MyD88/IL-1RAcP dependent in hTau mouse model of tauopathy. Finally, in Specific Aim 3, we will determine if blocking pTau by VLP-based immunotherapy reduces NF-kB priming and IL-1b maturation as well as restore memory in hTau mice. This successful outcome of this study will determine whether pTau triggers neuroinflammation via MyD88-NF-kB-NLRP3-ASC inflammasomes-IL-1b pathway. This will of high significance for the development and testing of the VLP-based pTau-targeted therapeutics against neuroinflammation in tauopathies.